When an engine carries out combustion under an oxygen excess atmosphere, the exhaust gas contains carbon monoxide, hydrocarbon and nitrogen oxides (NOx). Selective catalytic reduction (SCR) catalysts are known as catalysts that reduce the NOx which is discharged under an oxygen atmosphere, using ammonia or the like as a reducing agent.
PTL 1 describes a method for producing crystalline silicoaluminophosphate particles supporting an iron component, by spraying, drying and firing a dispersion obtained by mixing a ferrous sulfate aqueous solution and crystalline silicoaluminophosphate particles (Example 11 and elsewhere).
PTL 2 describes a nitrogen oxide purification catalyst supporting iron, cobalt, palladium, copper or the like on zeolite comprising at least silicon, aluminum and phosphorus as the skeletal structure (claim 1, paragraph [0079], and elsewhere).
PTL 3 describes a nitrogen oxide-adsorbed material supporting paramagnetic iron (III) ion on zeolite (claim 1 and elsewhere).